But now, with bold use of the veto pen and scorched-earth campaign rhetoric, Crist has estranged fellow Republicans and become a force to be feared in the Capitol.

His newfound aggressiveness — rooted in his own political survival — is leaving its mark on legislation that touches the lives of every Floridian: schoolchildren and teachers, homeowners, anyone who pays an electric bill and the growing ranks of Florida's poor.

Just a word of "concern'' from Crist's lips is enough to put a major bill like the House's Medicaid reform effort in jeopardy. His overt threat to veto a property insurance bill Wednesday resulted in the House shelving it. Some lawmakers fear he might even veto the entire $69 billion budget.

"Maybe they were surprised by the fact that I take the job of governor very, very seriously,'' Crist said. "And when there's a time to exercise the authority and the trust people put in you, you need to do it. And I'm going to keep doing it.''

The legislative session ends next Friday and the atmosphere is hostile. House Speaker Larry Cretul called Crist erratic this week, and other lawmakers suggest he's dishonest about the motivations for his vetoes.

The tone stands in contrast to last year, when one high-ranking legislator donned rose-colored glasses to mock Crist's optimism. Heading into this session, Crist's agenda and budget were written off by legislators. The governor was expected to veer to the right.

Instead, Crist vetoed education legislation that was a priority of former Gov. Jeb Bush. That ensured Bush would endorse Senate front-runner Marco Rubio. And it heightened the likelihood that Crist is positioning himself to leave the GOP primary, if not the party itself.

Republican legislative leaders felt betrayed by the veto. Crist and his advisers repeatedly said he would sign the bill linking teacher pay to student performance. After the veto, Crist angered legislators by calling the Capitol an ''asylum.''

Cretul, one of the most mild-mannered lawmakers, lashed out in a written statement, saying Crist produces little but ''poll-driven press releases'' and is ''never willing to step up and put good policy above campaign priorities.''

Cretul said he was endorsing Rubio, a former House speaker, because he stands in ''sharp contrast with his opponent's erratic behavior and his relentlessly negative and desperate attacks.''

Crist has exercised his veto power plenty in the past.

He trimmed a record $459 million from the 2007 budget. But he was rarely threatening, and he frequently praised lawmakers.

''When his poll numbers were good, the governor said we were in a 'golden era.' Now he's losing a Senate race and we're a bunch of people in an asylum,'' Sen. Don Gaetz, R-Niceville, quipped. "What's that tell you?''

Democrats noted a mood change in the Capitol after the education-bill veto. Crist had vetoed a Republican leadership campaign finance bill a few days earlier.

"Just in private conversations with leaders on the other side, they are practically obsessed with him,'' said Rep. Keith Fitzgerald, D-Sarasota. "Their anger toward him is real passion. But Crist went from being irrelevant to being at the center of the process.''

Cannon is pushing a major Medicaid overhaul that expands the control of managed care insurance companies in the hope of reducing costs and fraud in the program that serves 2.8 million Floridians.

On Tuesday, the day after the plan passed, Cannon met with key senators to brief them. About 50 minutes later, Sen. Joe Negron asked the question: "Do we know where Gov. Crist is on this plan?''

No one did.

The nursing union, SEIU, plans to urge Crist to veto the bill.

Crist has compared Medicaid reform to the education bill because he says it's being rushed through the process. He said he's concerned that the bill puts nursing homes and care for the developmentally disabled, the "most vulnerable,'' under HMOs.

To starve Crist of headline-grabbing vetoes, Republican legislators are dialing back some of their more controversial measures and offering an olive branch or two.

Sen. John Thrasher, R-St. Augustine, called for comity: "Let's finish this session on a high note.''

Still, though, the Senate is stalling the confirmation of two Crist appointees on the Public Service Commission, where they have helped stop large rate increases for Progress Energy and Florida Power & Light — major Republican Party contributors.

If the appointees aren't confirmed, it could hand Crist a potent weapon to campaign with populist zeal against the Legislature.

Ever since he took office in 2007, Crist has used populism as weapon, notably by demonizing the property insurance industry. This session, he threatened to veto an insurance bill, which stopped the legislation in its tracks Wednesday.

If the governor vetoes the budget, that would prompt a special lawmaking session, raise Crist's profile and antagonize the Legislature all the more.

And that's a possibility, according to Sen. Mike Fasano, a New Port Richey Republican and Crist's closest ally in the Legislature.

''He will have the final say or the last laugh. He could veto the entire budget, you know,'' Fasano said. ''Gov. Crist is a stronger governor now than he was when the session began.''

Staff writers Mary Ellen Klas and Steve Bousquet contributed.

Gov. Charlie Crist has wielded and threatened to wield his veto pen to great effect on high-profile issues:

• Education: Though he said he supported it and looked as if he'd sign it, Crist vetoed Senate Bill 6 — a high-priority piece of legislation.

• Leadership funds: Crist rejected this bill that officially established ''leadership funds'' controlled by top legislative lawmakers because he said they looked like ''slush funds.'' In response, future Senate President Mike Haridopolos wrote an angry letter, accusing the governor of not even reading the bill.

• Medicaid: Days after future House Speaker Dean Cannon withdrew his endorsement of the governor, the House passed Cannon's Medicaid reform bill. Crist said he's ''concerned'' with it because of the way HMOs would have a greater say over nursing homes and care for the developmentally disabled.

• Insurance: Crist founded his populism in the Legislature by taking on property-insurance companies. So it was no surprise he threatened to veto a bill that would have allowed the companies to more easily raise rates. The House shelved the bill Wednesday.

• Budget: Crist has been mum on what in the budget causes him concern. But top advisers like Sen. Mike Fasano of New Port Richey say it's possible that governor could reject the entire $69-billion-plus spending plan.